Cooling device

ABSTRACT

A cooling device includes a fan, a heat sink, and an attaching portion arranged to attach the fan to the heat sink. The fan includes an impeller rotating about a center axis, a motor arranged to rotate the impeller, and a base portion supporting the motor. The attaching portion includes a frame surrounding a portion of the impeller opposed to the heat sink, a plurality of supports projecting from the frame to a side opposite to the heat sink, and a plurality of supporting ribs connecting the supports and the base portion to each other, arranged about the center axis, and extending from the base portion away from the center axis. Each supporting rib has a first primary surface and a second primary surface arranged opposite to the impeller. The first and second primary surfaces are inclined with respect to a plane substantially perpendicular to the center axis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cooling device which cools a heat source.

2. Description of the Related Art

CPUs (Central Processing Units) incorporated in personal computers or servers include cooling devices attached to the CPUs for cooling the CPUs. An exemplary known cooling device is a device in which a heat sink and a fan are combined with each other. In this cooling device, the heat sink dissipates heat generated by the CPU by a plurality of heat-dissipating fins that are radially arranged, and the fan arranged on the opposite side of the heat sink to the CPU delivers air to the heat sink.

For example, US 2005/0253467 A1 describes a cooling device which includes an axial fan rotating about a rotation axis and a heat sink arranged on an air-discharge side of the axial fan. The heat sink includes a plurality of heat-dissipating fins arranged radially about the rotation axis of the axial fan. A motor-supporting member arranged to support a motor of the axial fan is provided on an air-intake side of an impeller of the axial fan, and is connected to an annular fan case, which covers only a portion of the axial fan near the heat sink, via three webs which are circumferentially spaced apart from each other on the air-intake side of the axial fan.

U.S. Pat. No. 7,052,236 B2 describes a cooling device that includes an axial fan and a housing covering the axial fan and that sends air to a heat source. In this air-sending device, an inner side surface of the housing is inclined with respect to a rotation axis of the axial fan on an air-discharge side or an air-intake side of the axial fan, so as to provide an air-flow guiding portion. A plurality of stationary vanes which connect the air-flow guiding portion and a base portion of a motor to each other are radially arranged about the rotation axis of the axial fan. With this configuration, the static pressure characteristics of the axial fan are improved.

The cooling device having the axial fan and the heat sink combined with each other, as described in US 2005/0253467 A1, must improve its cooling performance in order to accommodate an increase in heat generation caused by improvements in the CPU's performance. Moreover, that cooling device must also have a smaller operating sound in view of improvements in a working environment in which personal computers and servers are used, for example. For these reasons, in the performance evaluation of that cooling device, the cooling performance when the operation sound is set to be equal to or less than a predetermined limit level is compared. Therefore, if the operating sound of the cooling device can be reduced without reducing the number of revolutions of the axial fan, the number of revolutions of the axial fan which causes the operating sound of the limit level can be increased, thereby improving the cooling performance of the cooling device. Alternatively, by increasing the number of revolutions of the axial fan and reducing the cooling performance of the heat sink itself, the manufacturing cost of the heat sink can be reduced while maintaining the cooling performance of the cooling device.

However, in the cooling device described in US 2005/0253467 A1, the webs arranged in an approximately rectangular column are provided on the air-intake side of the impeller of the axial fan, and therefore, a relatively large interference sound is generated because of interference of an air flow created by rotation of the impeller with the webs. For this reason, a reduction of the operating sound of the cooling device is limited.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of the present invention provide a cooling device. The cooling device includes a fan, a heat sink, and an attaching portion which fixes the fan to the heat sink. The fan includes an impeller rotating about a rotation axis, a motor arranged to rotate the impeller, and a base portion supporting the motor, and creates an air flow by the rotation of the impeller. The heat sink is arranged at a location which receives the air flow from the fan, so as to be in contact with a heat source. The attaching portion includes a frame surrounding at least a portion of the impeller which is opposed to the heat sink, and a plurality of supports projecting from the frame toward a side of the frame opposite to the heat sink. The attaching portion further includes a plurality of supporting ribs which are arranged around a center axis, extend from the base portion away from the center axis, and are connected to the supports. Each supporting rib has a first primary surface opposed to the impeller and a second primary surface on a side opposite to the impeller. The first and second primary surfaces are inclined with respect to a plane substantially perpendicular to the center axis. In each of the first and second primary surfaces, a circumferential component from a downstream-side end thereof to an upstream-side end thereof in a rotation direction of the impeller is opposite to the rotation direction.

A thickness of a cross-section of each supporting rib substantially perpendicular to a longitudinal direction of the supporting rib is preferably thinner on both sides of a center thereof in a circumferential direction than at the center.

In at least one of the first and second primary surfaces, a normal angle thereof near the downstream-side end is in a range from approximately 20° to approximately 40°, when being averaged in a radial direction. Please note that the radial direction is substantially perpendicular to the center axis J1.

Each supporting rib may extend in a direction opposite to the rotation direction of the impeller as it extends away from the center axis. Moreover, each supporting rib may be curved so that it is convex along the rotation direction of the impeller.

An upstream-side surface of each support in the rotation direction of the impeller is preferably smooth and convex.

An inner side surface of the frame may have, at an end thereof opposite to the heat sink, an inclined surface which extends close to the center axis as it extends close to the heat sink. This inclined surface is preferably approximately annular about the center axis.

The heat sink preferably includes a plurality of heat-dissipating fins which are arranged around the center axis and extend along the center axis.

Other features, elements, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a cooling device according to a first preferred embodiment of the present invention.

FIG. 2 is a plan view of the cooling device according to the first preferred embodiment of the present invention.

FIG. 3 is a plan view of a heat sink in the cooling device of FIGS. 1 and 2.

FIG. 4 is a cross-sectional view of a supporting rib and a blade of an impeller axially closest thereto in the cooling device of FIGS. 1 and 2.

FIG. 5A is an enlarged view of a portion of the cooling device of FIGS. 1 and 2 in the vicinity of a support of a frame.

FIG. 5B is a cross-sectional view of the support.

FIG. 5C is a cross-sectional view of the frame.

FIG. 6 is a cross-sectional view of a supporting rib and a blade of an impeller axially closest thereto, in a cooling device according to a second preferred embodiment of the present invention.

FIGS. 7A, 7B, 7C, and 7D show other exemplary shapes of the supporting rib.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 through 7D, preferred embodiments of the present invention will be described in detail. It should be noted that in the explanation of preferred embodiments of the present invention, when positional relationships among and orientations of the different components are described as being up/down or left/right, the positional relationships and orientations shown in the drawings are indicated; positional relationships among and orientations of the components once having been assembled into an actual device are not indicated. Meanwhile, in the following description, an axial direction indicates a direction substantially parallel to a rotation axis, and a radial direction indicates a direction substantially perpendicular to the rotation axis.

FIRST PREFERRED EMBODIMENT

FIG. 1 is a perspective view of a cooling device 1 according to a first preferred embodiment of the present invention. FIG. 2 is a plan view of the cooling device 1.

The cooling device 1 of the present preferred embodiment is a heat sink fan including a heat sink 2 and a fan 3. The cooling device 1 is preferably attached to a heat source, e.g., a CPU (Central Processing Unit) in a personal computer or other electronic device, for example, and dissipates heat transferred from the heat source through the heat sink 2, thereby cooling the heat source.

As shown in FIGS. 1 and 2, the cooling device 1 includes the heat sink 2 that dissipates the heat transferred from the heat source, the fan 3 that delivers air to the heat sink 2 so as to cool the heat sink 2, an attaching portion 4 that fixes the fan 3 to the heat sink 2, and a fixing pin 5 arranged to attach the cooling device 1 to another device. In the present preferred embodiment, the fan 3 is an axial fan which delivers air approximately parallel to a center axis J1 by being rotated about the center axis J1. The cooling device 1 is attached such that a portion of the heat sink 2, which is located on a side opposite to the fan 3 in an axial direction, is in contact with the CPU. In the following description, for the sake of convenience, the fan 3 side and the heat sink 2 side in the axial direction are referred to as an upper side and a lower side, respectively. However, it is not necessary for the center axis J1 to be in the same direction as gravity.

FIG. 3 is a plan view of the heat sink 2. As shown in FIGS. 1 and 3, the heat sink 2 includes a plurality of heat-dissipating fins 22 defined by thin plates which are radially arranged around the center axis J1 of the fan 3 and extend along the center axis J1, a cylindrical fin-supporting portion 23 which connects the heat-dissipating fins 22 at inner radially portions thereof to each other, and a core 24 defined by a circular cylinder (shown in FIG. 3 only) which is inserted into the fin-supporting portion 23. A lower end portion of the core 24 (i.e., an opposite end portion to the fan 3 (see FIG. 2)) projects downward from lower ends of the heat-dissipating fins 22 and the fin-supporting portion 23, and a lower end surface of the core 24 is in contact with the CPU.

In the present preferred embodiment, the heat-dissipating fins 22 and the fin-supporting portion 23 shown in FIG. 3 are preferably made of aluminum (Al) or aluminum alloy so as to be integral with each other, while the core 24 is preferably made of copper (Cu), for example. In the following description, the combination of the heat-dissipating fins 22 and the fin-supporting portion 23 are referred to as a “fin unit 21.” Please note that the material of the core 24 is not limited to copper. For example, the core 24 may be made of aluminum or aluminum alloy. Moreover, the core 24 may be made of the same material as that of the fin unit. In this case, the core 24 may be integrally formed with the fin-supporting portion 23 when the fin unit is formed.

As shown in FIG. 3, in the present preferred embodiment, an outer side surface 211 of the fin unit 21 preferably is approximately cylindrical about the center axis J1. Please note that the outer side surface 211 of the fin unit 21 is preferably a surface formed by circumferentially connecting outer radially edges of the heat-dissipating fins 22. As shown in FIG. 1, two grooves 213 extending substantially perpendicularly to the center axis J1 are preferably provided on the outer side surface 211 of the fin unit 21. By engagement of an engagement portion 441 of the attaching portion 4 with the groove 213, the fan 3 is attached to the heat sink 2.

As shown in FIG. 3, each heat-dissipating fin 22 of the fin unit 21 extends outward from the fin-supporting portion 23 in a radial direction, i.e., a direction away from the center axis J1, and is curved. In the present preferred embodiment, each heat-dissipating fin 22 preferably is convex toward a counterclockwise direction in FIG. 3. Each heat-dissipating fin 22 includes an inner radial portion 221 connected to an outer side surface of the fin-supporting portion 23 and a radially outer portion 222 extending outward in the radial direction from a radially outer end of the radially inner portion 221, i.e., from an opposite end of the inner radial portion 221 to the fin-supporting portion 23. In the present preferred embodiment, the inner radial portion 221 is defined by a single thin plate, while the outer radial portion 222 is defined by two thin plates one of which circumferentially covers the other. The outer radial end of the inner radial portion 221 is located approximately at the center of the heat-dissipating fin 22 in the radial direction.

As shown in FIGS. 1 and 2, the fan 3 is arranged axially above the heat sink 2 and includes a stator portion 31 having a base portion 311 fixed to the heat sink 2 via the attaching portion 4, and a rotor portion 32 supported below the base portion 311 (i.e., on the heat sink 2 side of the fan 3) in a rotatable manner relative to the stator portion 31. In the present preferred embodiment, the base portion 311 of the stator portion 31 is defined by an approximately circular plate centered on the center axis J1. The diameter of the base portion 311 is approximately equal to the diameter of the core 24 of the heat sink 2 (see FIG. 3), when the base portion 311 is viewed along the axial direction.

The rotor portion 32 includes an impeller 322 which is made of resin in the present preferred embodiment. The impeller 322 includes a hollow hub 323 and a plurality of blades 324 arranged on an outer side surface of the hub 323 to extend outward in the radial direction, as shown in FIG. 1. In the present preferred embodiment, the hub 323 is approximately cylindrical about the center axis J1 and opens upward in the axial direction. In the present preferred embodiment, preferably seven blades 324, for example, are fixed on the outer side surface of the hub 323. The hub 323 and the blades 324 are preferably formed by injection molding, for example. When the hub 323 is viewed along the axial direction, the diameter thereof is approximately equal to the diameter of the base portion 311. Inside the hub 323 an armature and a field magnet which generate a torque about the center axis J1 and a bearing unit which supports the rotor portion 32 in a rotatable manner relative to the stator portion 31 are provided.

When the fan 3 is driven, the impeller 322 of the rotor portion 32 is rotated about the center axis J1 in a clockwise direction in FIG. 1 and sends air toward the heat sink 2. In other words, an air flow from the base portion 311 of the stator portion 31 to the rotor portion 32 is created, and the heat sink 2 receives the air flow from the fan 3.

The attaching portion 4 includes a frame 41 above the heat sink 2 surrounding a lower portion of the impeller 322, i.e., a portion of the impeller 322 which is opposed to the heat sink 2, as shown in FIGS. 1 and 2. The frame 41 is approximately annular about the center axis J1, for example. As shown in FIG. 1, the axial height of the frame 41 is less than the axial height of the impeller 322 of the fan 3 in the present preferred embodiment. Thus, an axially upper portion of the impeller 322 (i.e., a portion of the impeller 322 other than the aforementioned lower portion thereof) is exposed axially above the frame 41.

The attaching portion 4 further includes a plurality of supports 42 projecting from the frame 41 toward a side opposite to the heat sink 2, i.e., upward, a plurality of supporting ribs 43 extending from the base portion 31 of the fan 3 outward in the radial direction, i.e., away from the center axis J1, and a plurality of rotation restricting portions 44 projecting downward from the frame 41 along the outer side surface 211 of the fin unit 21. The rotation restricting portions 44 prevent rotation of the attaching portion 4 relative to the heat sink 2 when the fan 3 is attached to the heat sink 2. In the present preferred embodiment, four rotation restricting portions 44 are provided. Two of the rotation restricting portions 44 which are opposed to each other are provided with engagement portions 441 which are to engage with two grooves 213 on the outer side surface 211 of the fin unit 21, respectively. Each rotation restricting portion 44 supports the fixing pin 5.

In the cooling device 1, preferably four supports 42 and four supporting ribs 43, for example, provided in the attaching portion 4 are arranged around the center axis J1 at approximately regular angular intervals in the circumferential direction, as shown in FIG. 1. As shown in FIGS. 1 and 2, each supporting rib 43 is inclined so that it extends in an opposite direction (i.e., to a counterclockwise direction in FIGS. 1 and 2) to the rotation direction of the impeller 322 as it extends away from the center axis J1. Moreover, each supporting rib 43 is curved so as to be convex along the rotation direction of the impeller 322 (i.e., a clockwise direction in FIGS. 1 and 2). In other words, a direction from the supporting rib 43 to a straight line which connects a base portion 311 side end of the supporting rib 43 and a support 42 side end of the supporting rib 43 to each other extends in a direction that is opposite to the rotation direction of the impeller 322.

FIG. 4 is a cross-sectional view of one supporting rib 43 and a blade 324 disposed closest thereto, taken along a cylindrical plane centered on the center axis J1 near the center of the supporting rib 43 in the radial direction. In FIG. 4, the rotation direction of the impeller 322 is a direction from the right to the left in FIG. 4. (This is the same in FIGS. 6, 7A, 7B, 7C, and 7D.) The other supporting ribs 43 and the other blades 324 preferably also have substantially the same shapes as those of the supporting rib 43 and the blade 324 shown in FIG. 4, respectively.

The cross section of the supporting rib 43 shown in FIG. 4 (i.e., the cross section substantially perpendicular to the longitudinal direction of the supporting rib 43 which extends from the base portion 311 to the support 42 in FIG. 1) is thick at a center in FIG. 4 (which corresponds to the center of the cross section in the circumferential direction), and is thin on both sides of the center, i.e., on the right and left of the center in FIG. 4. The supporting rib 43 has a first primary surface 431 opposed to the impeller 322 of the fan 3 and a second primary surface 432 which is on the opposite side of the supporting rib 43 from the first primary surface 431. The first primary surface 431 and the second primary surface 432 are not parallel to a plane that is substantially perpendicular to the center axis J1, i.e., are inclined or curved with respect to that plane. The first primary surface 431 is located behind the second primary surface 432 (i.e., on the right of the second primary surface 432 in FIG. 4) in the rotation direction of the impeller 322. In the present preferred embodiment, in the cross section of the supporting rib 43 shown in FIG. 4, the first primary surface 431 is approximately straight while the second primary surface 432 is curved.

The first primary surface 431 has a leading (downstream-side) end 433 and a trailing (upstream-side) end 434 in the rotation direction. Those ends 433 and 434 are hereinafter referred to as the downstream-side end 433 and the upstream-side end 434 of the first primary surface 431 in the following description. Similarly, the second primary surface 432 also has a downstream-side end and an upstream-side end. In the present preferred embodiment, the downstream-side end of the second primary surface 432 is substantially coincident with the downstream-side end 433 of the first primary surface 431, and is located ahead of (on the downstream side of) the upstream-side end 434 a of the second primary surface 432 in the rotation direction. In other words, in each of the first primary surface 431 and the second primary surface 432 of the supporting rib 43, a circumferential component from the downstream-side end 433 to the upstream-side end 434 or 434 a is opposite to the rotation direction of the impeller 322.

A normal angle of the first primary surface 431 of each supporting rib 43 at the downstream-side end 433 thereof with respect to the center axis J1 (hereinafter, referred to as a normal angle of the first primary surface 431) is preferably in a range from approximately 20° to approximately 40°, when being averaged in the radial direction of that supporting rib 43. “Normal angle” as used in the specification is defined as the angle between the center axis J1 and a line extending in a direction that is perpendicular to the first primary surface 431. In the present preferred embodiment, that angle is approximately 30°. Where a downstream-side portion of each supporting rib 43 in the rotation direction is chamfered in the cross section shown in FIG. 4, the normal angle of the first primary surface 431 is a normal angle thereof at an end of the chamfered portion which is adjacent to the upstream-side end 434, i.e., at the boundary between the chamfered portion and the first primary surface 431 with respect to the center axis J1.

The shape of the blades 324 of the impeller 322 is described. Each blade 324 has a primary surface 3241 opposed to the supporting ribs 43, i.e., an upper primary surface 3241, and a primary surface 3242 which is on the opposite side of the blade 324 from the supporting ribs 43, i.e., a lower primary surface 3242. Hereinafter, the primary surfaces 3241 and 3242 are referred to as a blade upper surface 3241 and a blade lower surface 3242, respectively. As shown in FIG. 4, the blade upper surface 3241 and the blade lower surface 3242 of each blade 324 are inclined in a direction opposite to the inclination direction of the first primary surface 431 and the second primary surface 432 of the supporting rib 43. In other words, each blade 324 is inclined in a direction opposite to the inclination direction of the supporting rib 43.

A supporting rib 43 side end 3243 of the blade 324 is located ahead of (i.e., on the downstream side of) the other end 3244 in the rotation direction of the impeller 3222. Thus, the supporting rib 43 side end 3243 of the blade 324 and the other end 3244 thereof are respectively referred to as a blade leading edge 3243 and a blade trailing edge 3244 in the following description. In the cooling device 1, when the impeller 322 is rotated, the blade leading edge 3243 of each blade 324 passes below the upper edges 434 and 434 a of each supporting rib 43 prior to passing below the lower edge 433 of that supporting rib 43.

In each blade 324, a normal angle of the blade upper surface 3241 at or near the blade leading edge 3243 of the blade upper surface 3241 with respect to the center axis J1 (hereinafter, referred to as a normal angle of the blade upper surface 3241) is preferably in a range from approximately 20° to approximately 40°, when being averaged in the radial direction. In the present preferred embodiment, the normal angle of the blade upper surface 3241 is approximately 30°.

Next, the structure of the frame 41 is described. FIG. 5A is an enlarged view of a portion around one of the supports 42 of the attaching portion 4. FIG. 5B is a cross-sectional view of the portion of the support 42 shown in FIG. 5A near the frame 41, taken along a plane substantially perpendicular to the center axis J1. FIG. 5C is a cross-sectional view of the frame 41 shown in FIG. 5, taken along a plane including the center axis J1 and substantially parallel to the center axis J1.

In the present preferred embodiment, an upstream-side surface 421 of each support 42 in the rotation direction of the impeller 322 is smooth and convex. For example, the upstream-side surface 421 is round and chamfered, as shown in FIGS. 5A and 5B. An inner side surface 411 of the frame 41 (i.e., a center axis J1 side surface thereof) has an inclined surface 412 at an end thereof opposite to the heat sink 2, i.e., at an end adjacent to the supports 42 and the supporting ribs 43, as shown in FIG. 5C. The inclined surface 412 is arranged such that it extends close to the center axis J1 as it extends close to the heat sink 2. Where the frame 41 is approximately annular about the center axis J1, the inclined surface 412 is also approximately annular about the center axis J1.

As described above, in the cooling device 1, each of the first primary surface 431 and the second primary surface 432 of each supporting rib 43 of the attaching portion 4 which fixes the fan 3 to the heat sink 2, is inclined with respect to a plane substantially perpendicular to the center axis J1. A circumferential component from the downstream-side end 433 of each supporting rib 43 to the upstream-side end 434 or 434 a is in a direction opposite to the rotation direction of the impeller 322. Moreover, the first primary surface 431 and the second primary surface 432 of each supporting rib 43 are inclined in a direction opposite to the inclination direction of the blade upper surface 3241 and the blade lower surface 3242 of each blade 324 of the impeller 322.

When the fan 3 is rotated, air taken in from the supporting rib 43 side of the impeller 322 flows into the impeller 322 toward the blade upper surfaces 3241 of the blades 324. Since the first primary surface 431 and the second primary surface 432 of the supporting rib 43 are inclined in a direction opposite to the inclination direction of the blade upper surface 3241 of the blade 324 as described above, the first primary surface 431 and the second primary surface 432 can be arranged approximately parallel to the air flow flowing into the impeller 322, thereby reducing interference between the supporting ribs 43 and the air flow and reducing the operating sound of the cooling device 1 including the interference sound generated at the supporting ribs 43.

Thus, the number of revolutions of the impeller 322 can be increased without increasing the operation sound of the cooling device 1, resulting in an increase in the volume of the air supplied to the heat sink 2 from the fan 3. Consequently, the cooling performance of the cooling device 1 is improved. Alternatively, it is possible to reduce the cooling performance of the heat sink 2 itself without reducing the cooling performance of the cooling device 1. Therefore, the volume of the core 24 in the heat sink 2 can be reduced, resulting in a weight reduction of the cooling device 1 and a reduction of the manufacturing cost.

Since each supporting rib 43 preferably has a blade-shaped cross section when cut along a plane substantially perpendicular to the longitudinal direction thereof, interference of the air flow flowing into the impeller 322 with the supporting ribs 43 is further reduced, thus further reducing the operating sound of the cooling device 1 caused by the supporting ribs 43. Moreover, the interference of the air flow flowing into the impeller 322 with the supporting ribs 43 can be further reduced by setting the average of the normal angle of the first primary surface 431 in the radial direction to be in a range from approximately 20° to approximately 40°. Thus, the operating sound of the cooling device 1 generated by the supporting ribs 43 is further reduced.

If each supporting rib is provided approximately parallel to the blade leading edge of one blade of the impeller when being arranged circumferentially adjacent to that blade leading edge, interference between the blade leading edge and the supporting rib occurs over substantially the entire length of the supporting rib, thus increasing the interference sound.

However, in the cooling device 1 of the present preferred embodiment, the supporting ribs 43 are inclined so that they extend toward the opposite direction to the rotation direction of the impeller 322 as they extend away from the center axis J1. Therefore, an angle formed by each supporting rib 43 and the blade leading edge 3243 of the blade 324 of the impeller 322 when the supporting rib 43 crosses the blade leading edge 3243 (i.e., an angle which is assumed to be zero when the supporting rib 43 is substantially parallel to the blade leading edge 3243, with the intersection of the blade leading edge 3243 and the supporting rib 43 used as a reference) is increased. Thus, at every instant during rotation of the impeller 322, instantaneous generation of a large interference sound is prevented by reducing the intersection of the supporting rib 43 and the blade leading edge 3243. Consequently, the generation of a large interference sound caused by interference between the supporting rib 43 and the blade leading edge 3243 over substantially the entire length of the supporting rib 43 is prevented, resulting in a further reduction of the operating sound of the cooling device 1 caused by the supporting ribs 43.

Moreover, since each supporting rib 43 is preferably curved to be convex along the rotation direction of the impeller 322, the angle formed between each supporting rib 43 and the blade leading edge 3243 of the blade 324 of the impeller 322 when the supporting rib 43 and the blade leading edge 3243 cross each other is further increased. Consequently, at every instant during the rotation of the impeller 322, the instantaneous generation of a large interference sound is prevented by reducing the intersection of the supporting rib 43 and the blade leading edge 3243. Accordingly, the operating sound of the cooling device 1 generated by the supporting ribs 43 is further reduced.

As described above, the upper portion of the impeller 322 is exposed above the frame 41 in the cooling device 1 of the present preferred embodiment. Thus, when the fan 3 is driven, air can be taken in from the surroundings of the impeller 322 (i.e., from between three supports 42 arranged in the circumferential direction). Therefore, the volume of air delivered to the heat sink 2 can be increased and the cooling performance of the cooling device 1 can be further improved.

Air taken in from the surroundings of the impeller 322 flows into the impeller 322 from between three supports 42 in a clockwise direction in FIG. 1 which is along the rotation direction of the impeller 322. Since the upstream-side surface 421 of each support 42 in the rotation direction of the impeller 322 is smooth and convex in the attaching portion 4, as shown in FIGS. 5A and 5B, interference of the air flow flowing from the surroundings of the impeller 322 with the support 42 is reduced, thus reducing the operating sound of the cooling device 1 including the interference sound generated at the supports 42.

As shown in FIG. 5C, in the attaching portion 4, the inclined surface 412 is provided at an end of the inner side surface 411 of the frame 41 opposed to the heat sink 2. The inclined surface 412 extends closer to the center axis J1 as it extends closer to the heat sink 2. With this configuration, interference of the air flow flowing from the surroundings of the impeller 322 with the frame 41 is further reduced. Therefore, the operating sound of the cooling device 1 including the interference sound generated at the frame 41 is further reduced. Moreover, due to an air-collecting effect of the frame 41, the volume of the air delivered to the heat sink 2 is increased, thus further improving the cooling performance of the cooling device 1.

In the cooling device 1 of the present preferred embodiment, the heat sink 2 includes a plurality of heat-dissipating fins 22 defined by thin plates which are radially arranged around the center axis J1 and extend along the center axis J1. Thus, it is possible to increase the total surface area of the heat-dissipating fins 22 without increasing the size of the fin unit 21, and/or without excessively reducing the thickness of each heat-dissipating fin in order to increase the number of the heat-dissipating fins, thus ensuring that each of the heat-dissipating fins 22 is sufficiently strong. Consequently, the cooling performance of the heat sink 2 itself and the cooling performance of the cooling device 1 are improved. Moreover, a portion of each heat-dissipating fin 22 radially outside the center thereof is split into a plurality of thin plates one of which covers the other in the circumferential direction and which define the outer radial portion 222. Therefore, the total surface area of the heat-dissipating fins 22 is further increased, thus further improving the cooling performance of the heat sink 2 and the cooling device 1.

SECOND PREFERRED EMBODIMENT

A cooling device according to a second preferred embodiment of the present invention is now described. The cooling device of the present preferred embodiment has substantially the same structure as the cooling device 1 of the first preferred embodiment shown in FIGS. 1 and 2, except for the cross-sectional shape of the supporting rib. Thus, except for the supporting ribs, the components of the present preferred embodiment are labeled with same reference characters as those used in the first preferred embodiment and the detailed description thereof is omitted.

FIG. 6 is a cross-sectional view corresponding to FIG. 4, and illustrates a cross section of one supporting rib 43 a and a cross section of one of blades 324 of the impeller 322 which is axially closest to that supporting rib 43 a in the cooling device of the present preferred embodiment, taken along a cylindrical plane centered on the center axis J1 near the radial center of that supporting rib 43 a.

As shown in FIG. 6, the supporting rib 43 a has a flat plate shape having an approximately constant thickness. The first primary surface 431 and the second primary surface 432 of the supporting rib 43 a define substantially straight lines in the cross section of the supporting rib 43 a which is substantially perpendicular to the longitudinal direction thereof. In the supporting rib 43 a, the first primary surface 431 is inclined with respect to a plane substantially perpendicular to the center axis J1 so that a circumferential component from a downstream-side end 433 thereof to an upstream-side end 434 thereof is in a direction opposite to the rotation direction of the impeller 322, as in the first preferred embodiment. Moreover, the second primary surface 432 is inclined with respect to a plane substantially perpendicular to the center axis J1 so that a circumferential component from a downstream-side end 433 a to an upstream-side end 434 a is in a direction opposite to the rotation direction of the impeller 322. The first primary surface 431 is located behind the second primary surface 432 in the rotation direction of the impeller 322.

Since the first primary surface 431 and the second primary surface 432 of the supporting rib 43 a are inclined in a direction opposite to the blade upper surface 3241 of the blade 324 of the impeller 322 as described above, interference of an air flow flowing into the impeller 322 with the supporting ribs 43 a is reduced, thus reducing the operating sound of the cooling device generated by the supporting ribs 43 a, as in the first preferred embodiment.

Moreover, in each supporting rib 43 a, the average in the radial direction of the normal angle of the first primary surface 431, i.e., the normal angle of the first primary surface 431 adjacent to the downstream-side end 433 with respect to the center axis J1 is preferably in a range from approximately 20° to approximately 40°, as in the first preferred embodiment. Thus, the interference of the air flow flowing into the impeller 322 with the supporting rib 43 a is further reduced, and therefore, the operating sound of the cooling device 1 generated by the supporting ribs 43 b is further reduced. In addition, the average in the radial direction of the normal angle of the second primary surface 432, i.e., the normal angle of the second primary surface 432 near the downstream-side end 433 a with respect to the center axis J1 is preferably in a range from approximately 20° to approximately 40°. Thus, the operating sound of the cooling device 1 generated by the supporting ribs 43 a is further reduced.

The cooling devices according to the preferred embodiments of the present invention have been described above. However, the cross-sectional shape of the supporting rib in the attaching portion 4 of the cooling device is not limited to those shown in FIGS. 4 and 6. For example, the supporting ribs may have cross-sectional shapes as shown in FIGS. 7A, 7B, 7C, and 7D.

The cross section of the supporting rib 43 b substantially perpendicular to the longitudinal direction thereof, shown in FIG. 7A, has a blade shape in which the thickness thereof is relatively thick at a center in the circumferential direction and is thinner on both sides of the center in the circumferential direction, as in the supporting rib 43 shown in FIG. 4. However, the supporting rib 43 b is different from the supporting rib 43 shown in FIG. 4 in that the downstream-side end 433 and the upstream-side end 434 of the first primary surface 431 are spaced apart from the downstream-side end 433 a and the upstream-side end 434 a of the second primary surface 432, respectively.

The supporting rib 43 c shown in FIG. 7B has a plate shape in which the thickness is approximately constant. The first primary surface 431 and the second primary surface 432 are curved in the cross section of the supporting rib 43 c that is substantially perpendicular to the longitudinal direction thereof.

In the supporting rib 43 d shown in FIG. 7C, in the cross section that is substantially perpendicular to the longitudinal direction of the supporting rib 43 d, the first primary surface 431 is curved while the second primary surface 432 is approximately linear.

The cross section of the supporting rib 43 e substantially perpendicular to the longitudinal direction thereof, shown in FIG. 7D, preferably has an approximately oval blade shape in which the thickness is relatively large at a center in the circumferential direction and is smaller on both sides of the center in the circumferential direction.

Even if the supporting rib has any one of the cross-sectional shapes shown in FIGS. 7A, 7B, 7C, and 7D, the first primary surface 431 and the second primary surface 432 are inclined with respect to a plane substantially perpendicular to the center axis J1 in the cooling device of another preferred embodiment of the present invention so that a circumferential component from the downstream-side end 433 or 433 a to the upstream-side end 434 or 434 a is in a direction opposite to the rotation direction of the impeller 322. With this configuration, the operating sound of the cooling device generated by the supporting ribs is reduced, as in the first and second preferred embodiments.

In the aforementioned first and second preferred embodiments, both the first primary surface and the second primary surface of the supporting rib preferably are inclined with respect to a plane substantially perpendicular to the center axis. However, it is not necessary that both the first primary surface and the second primary surface are inclined. Instead, only one of the first primary surface and the second primary surface may be inclined. The interference of the air flow flowing into the impeller with the supporting ribs can be reduced if at least one of the first primary surface and the second primary surface of the supporting rib is inclined. Thus, a reduction of the operating sound of the cooling device, a weight reduction of the cooling device, and a reduction of the manufacturing cost of the cooling device, which have been described above, can be achieved.

Moreover, where only one of the first primary surface and the second primary surface is inclined, the inclination angle of the first primary surface or the second primary surface of the supporting rib with respect to the center axis can be set to be in a range from approximately 20° to approximately 40°.

The number of the supporting ribs 43 in the attaching portion 4 is not limited to four which is the number described in the first and second preferred embodiments. Five or more supporting ribs may be provided, for example. Moreover, the entire inner side surface 411 of the frame 41 may be inclined with respect to the center axis J1. In this case, the inner side surface 411 may have an approximately annular inclined surface which extends closer to the center axis J1 as it extends closer to the heat sink 2. Furthermore, it is not necessary that the frame 41 surrounds the entire circumference of the impeller 322. The frame 41 may have a shape obtained by cutting out a portion of an annular shape, as long as the frame 41 is arranged to surround the portion of the impeller 322 which is opposed to the heat sink 2.

As described above, according to the cooling device of the preferred embodiments of the present invention, the operating sound generated by the supporting ribs, the operating sound generated by the supports, and the operating sound generated by the frame are reduced. Moreover, the cooling performance of the cooling device is improved.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1-9. (canceled)
 10. A cooling device comprising: a fan including an impeller rotatable about a center axis of the fan, a motor arranged to rotate the impeller, and a base portion arranged to support the motor, the fan creating an air flow by rotation of the impeller; a heat sink arranged at a location which receives the air flow from the fan to be in contact with a heat source; and an attaching portion arranged to fix the fan to the heat sink; wherein the attaching portion includes: a frame surrounding at least a portion of the impeller that is opposed to the heat sink; a plurality of supports projecting from the frame to a side opposite to the heat sink; and a plurality of supporting ribs arranged around the center axis of the fan, which extend from the base portion away from the center axis, and which connect to the supports; each of the supporting ribs includes a first primary surface opposed to the impeller and a second primary surface which is opposite to the impeller, the first primary surface and the second primary surface being inclined with respect to a plane substantially perpendicular to the center axis; and in each of the first primary surface and the second primary surface, a circumferential component extending from a downstream-side end to an upstream-side end of the supporting ribs in a rotation direction of the impeller is in a direction opposite to the rotation direction of the impeller.
 11. The cooling device according to claim 10, wherein a cross section of each of the supporting ribs substantially perpendicular to a longitudinal direction thereof is thinner on both sides of a center in a circumferential direction than at the center.
 12. The cooling device according to claim 10, wherein a normal angle of at least one of the first primary surface and the second primary surface near the downstream-side end thereof with respect to the center axis is in a range from approximately 20° to approximately 40°, when being averaged in a radial direction substantially perpendicular to the center axis.
 13. The cooling device according to claim 10, wherein each of the supporting ribs extends in a direction opposite to the rotation direction of the impeller as it extends away from the center axis.
 14. The cooling device according to claim 13, wherein each of the supporting ribs is curved so as to be convex along the rotation direction of the impeller.
 15. The cooling device according to claim 10, wherein an upstream-side surface of each of the supports in the rotation direction of the impeller is smooth and convex.
 16. The cooling device according to claim 10, wherein an inner side surface of the frame includes, at an end the inner side surface opposite to the heat sink, an inclined surface which extends closer to the center axis as it extends closer to the heat sink.
 17. The cooling device according to claim 16, wherein the inclined surface is approximately annular around the center axis.
 18. The cooling device according to claim 10, wherein the heat sink includes a plurality of heat-dissipating fins which are arranged around the center axis and extend along the center axis. 